Laser irradiation apparatus and method for manufacturing semiconductor device

ABSTRACT

It is an object of the present invention to provide a laser irradiation apparatus being able to irradiate the irradiation object with the laser beam having homogeneous energy density without complicating the optical system. The laser irradiation apparatus of the present invention comprises a laser oscillator, an optical system for scanning repeatedly a beam spot of the laser beam emitted from the laser oscillator in a uniaxial direction over the surface of the irradiation object, and a position controlling means for moving the position of the irradiation object relative to the laser beam in a direction perpendicular to the uniaxial direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a laser irradiation apparatus used forcrystallizing a semiconductor film. Moreover, the present inventionrelates to a method for manufacturing a semiconductor device.

2. Related Art

A thin film transistor (TFT) formed using a poly-crystallinesemiconductor film is higher in mobility by double digits or more than aTFT formed using an amorphous semiconductor film, and has an advantagethat a pixel portion and a peripheral driver circuit in a semiconductordisplay device can be integrally formed over the same substrate. Thepoly-crystalline semiconductor film can be formed over an inexpensiveglass substrate by employing a laser annealing method.

As laser oscillators used in the laser annealing method, there are apulsed laser oscillator and a continuous wave laser oscillator accordingto the oscillation method. The pulsed laser oscillator typified by anexcimer laser has output power per unit time which is approximately 3 to6 digits higher than that of the continuous wave laser oscillator.Therefore, the throughput of the laser irradiation can be increased byshaping a beam spot (an irradiation region irradiated with the laserbeam in fact on the surface of the irradiation object) into arectangular spot having a length of several cm on a side or a linearspot having a length of 100 mm or more with the use of an opticalsystem. For this reason, the pulsed laser oscillator has been mainlyemployed for crystallizing the semiconductor film.

It is noted that a term of “linear” herein used does not mean a line ina strict sense but means a rectangle (or long ellipse) having a largeaspect ratio. For example, a rectangular beam having an aspect ratio of2 or more (preferably 10 to 10000) is referred to as a linear beam. Itis to be noted that the linear is included in the rectangular.

The semiconductor film crystallized thus by the pulsed laser beamincludes plenty of crystal grains whose positions and sizes are random.Unlike the inside of the crystal grain, an interface between the crystalgrains (a crystal grain boundary) includes an infinite number oftrapping centers and recombination centers due to the crystal defect orthe amorphous structure. When the carrier is trapped in the trappingcenter, the potential of the crystal grain boundary increases andbecomes a barrier against the carrier; therefore, the transportingproperty of the carrier decreases.

In view of the above problem, a technique relating to thecrystallization of the semiconductor film with the use of the continuouswave laser has attracted attention recently. In the case of thecontinuous wave laser, unlike the conventional pulsed laser, when thelaser beam is scanned in one direction to irradiate the semiconductorfilm, it is possible to grow a crystal continuously in the scanningdirection and to form an aggregation of crystal grains including asingle crystal extending long in the scanning direction.

To increase the throughput of the laser annealing, it is necessary toshape the continuous wave laser beam into linear by an optical system.The important point in shaping the laser beam is the homogeneity of theenergy density distribution of the beam spot in a major-axis direction(also referred to as a long-side direction). The energy densitydistribution in the major-axis direction affects the crystallinity ofthe semiconductor film crystallized by the laser annealing, and moreoveraffects the characteristic of a semiconductor element formed using thesemiconductor film crystallized thus. For example, when the beam spothas Gaussian energy density distribution in the major-axis direction,the characteristic of the semiconductor element formed using such a beamspot also varies so as to have the Gaussian distribution. Therefore, inorder to secure the homogeneity of the characteristic of thesemiconductor element, it is desirable to homogenize the energy densitydistribution of the beam spot in the major-axis direction. The beam spothaving homogeneous energy density distribution in the major-axisdirection has an advantage of high throughput because the beam spot canbe made longer in the major-axis direction.

To homogenize the energy density of the linear beam spot in themajor-axis direction, it is necessary to use an optical element such asa cylindrical lens or a diffractive optical element. However, theseoptical elements for homogenizing the energy density have a problem inthat the adjustment is complicate because they require advanced opticaldesign in consideration of a wavefront and a shape of the beam spot.

Moreover, the semiconductor film can be crystallized more effectivelywhen the absorption coefficient of the laser beam to the semiconductorfilm is higher. In the case of a YAG laser or a YVO₄ laser, the secondharmonic has higher absorption coefficient than the fundamental wave toa silicon film having a thickness of several tens to several hundred nm,which is usually used in a semiconductor device. Therefore, usually, theharmonic having shorter wavelength than the fundamental wave is used inthe laser crystallization for manufacturing a semiconductor device, andthe fundamental wave is hardly used. The harmonic can be obtained byconverting the fundamental wave by the non-linear optical element.

However, the continuous wave laser has lower output power per unit timethan the pulsed laser. Therefore, the density of photon to time is alsolow, and the conversion efficiency into the harmonic by the non-linearoptical element is also low. Specifically, in contrast with the pulsedlaser having a conversion efficiency of approximately 10 to 30%, thecontinuous wave laser has the conversion efficiency of approximately 0.2to 0.3%. The continuous wave laser has another problem in that theresistance of the non-linear optical element is much lower than that inthe pulsed laser because the continuous wave laser continuously givesburden to the non-linear optical element.

Therefore, a laser beam having the harmonic emitted from the continuouswave laser per unit time has low power, and it is difficult to increasethe throughput by enlarging the area of the beam spot, compared with thepulsed laser beam. For example, a continuous wave YAG laser can providethe fundamental wave with an output power as high as 10 kW but providethe second harmonic with output power as low as 10 W. In this case, thearea of the beam spot must be narrowed as small as 10⁻³ mm² in order toobtain the energy density required to crystallize the semiconductorfilm. As thus described, the continuous wave laser is inferior to thepulsed excimer laser in throughput, and this is one factor to decreasethe economical efficiency in mass production.

SUMMARY OF THE INVENTION

In view of the above problems, it is an object of the present inventionto provide a laser irradiation apparatus which can irradiate anirradiation object with a linear beam spot having homogeneous energydensity in the major-axis direction without complicating the opticalsystem. It is another object of the present invention to provide a laserirradiation apparatus which can grow continuously the crystal graintoward a direction perpendicular to a major axis of the linear beamspot. It is another object of the present invention to provide a laserirradiation apparatus which can increase the throughput of the laserirradiation to the irradiation object.

In view of the above problems, it is an object of the present inventionto provide a method for manufacturing a semiconductor device which canirradiate a semiconductor film with a linear beam spot havinghomogeneous energy density in the major-axis direction withoutcomplicating the optical system. It is another object of the presentinvention to provide a laser irradiation apparatus which can growcontinuously the crystal grain toward a direction perpendicular to amajor axis of the linear beam spot. It is another object of the presentinvention to provide a method for manufacturing a semiconductor devicewhich can increase the throughput of the laser irradiation to thesemiconductor film.

According to one feature of the present invention, a laser beam emittedfrom a laser oscillator is scanned with high speed in a uniaxialdirection by an optical system so as to form a quasi-linear beam spot.In this specification, the quasi-linear beam spot is a beam spot formedby scanning the laser beam along a line connecting a first point and asecond point. More specifically, the quasi-linear beam spot is a beamspot formed by scanning a laser beam on the second point before a regionmelted by irradiating the first point with the laser beam is solidified.Therefore, the region irradiated with the quasi-linear beam is meltedfor a predetermined period as if it is irradiated with the linear beam.

The laser beam is scanned by the optical system or the moving means formoving a position of the irradiation object relative to the opticalsystem and the laser beam so that the laser beam is scanned along eachof plural straight lines arranging at uniform intervals. A firstquasi-linear beam spot and a second quasi-linear beam spot which areformed by scanning the laser beam along the adjacent straight linesamong the plural straight lines overlap partially each other in adirection perpendicular to the major axes of the quasi-linear beamspots. Moreover, the second quasi-linear beam spot is formed by scanningthe laser beam before the part of the irradiation object irradiated withthe first quasi-linear beam spot is solidified. Accordingly, the crystalgrain in the irradiation object can be extended in the directionperpendicular to the major axis of the quasi-linear beam.

The present invention discloses a laser irradiation apparatus comprisinga laser oscillator, an optical system for forming a quasi-linear beamspot by scanning a laser beam emitted from the laser oscillator so as tomove back and forth along a straight line, and moving means for moving aposition of an irradiation object relative to the laser beam in adirection perpendicular to the major axis of the quasi-linear beam spot.In this laser irradiation apparatus, the irradiation object is moved bythe moving means so that a first irradiation region, which is irradiatedwith the quasi-linear beam spot, overlaps partially a second irradiationregion, which is irradiated with the quasi-linear beam spot after thefirst irradiation region is irradiated. Moreover, in this laserirradiation apparatus, before the first irradiation region melted by thequasi-linear laser beam is solidified by absorbing a laser beamdelivered to a part of the quasi-linear beam spot, the irradiationposition of the quasi-linear beam spot is moved by the moving means fromthe first irradiation region to the second irradiation region.

The present invention discloses a laser irradiation apparatus comprisinga laser oscillator, an optical system for scanning a laser beam emittedfrom the laser oscillator so as to move back and forth along a straightline, and moving means for moving a position of an irradiation objectrelative to the laser beam in a direction perpendicular to the scanningdirection of the laser beam. In this laser irradiation apparatus, thelaser beam is scanned along a wave-like line or a saw-like line on theirradiation object. When the laser beam is scanned along the wave-likeline or the saw-like line from a first direction-turning point to athird direction-turning point through the second direction-turningpoint, a first beam spot formed by irradiating the firstdirection-turning point with the laser beam overlaps partially a secondbeam spot formed by irradiating the third direction-turning point withthe laser beam. Moreover, the laser beam is scanned from the firstdirection-turning point to the third direction-turning point before thepart of the irradiation object irradiated with the first beam spot issolidified.

The present invention discloses another laser irradiation apparatuscomprising a laser oscillator and an optical system for scanning a laserbeam emitted from the laser oscillator along each of plural straightlines arranging at uniform intervals. In this laser irradiationapparatus, a first quasi-linear beam spot formed by scanning the laserbeam along a first straight line among the straight lines overlapspartially a second quasi-linear beam spot formed by scanning the laserbeam along a second straight line adjacent to the first straight line.Moreover, the second quasi-linear beam spot is formed by scanning thelaser beam before the part of the irradiation region irradiated with thefirst quasi-linear beam spot is solidified.

The present invention discloses another laser irradiation apparatuscomprising a laser oscillator and an optical system for scanning a laserbeam emitted from a laser oscillator along a wave-like line or asaw-like line. In this laser irradiation apparatus, when the laser beamis scanned along the wave-like line or the saw-like line from a firstdirection-turning point to a third direction-turning point through asecond direction-turning point, a first beam spot centering on the firstdirection-turning point overlaps partially a second beam spot centeringon the third direction-turning point. Moreover, the laser beam isscanned from the first direction-turning point to the thirddirection-turning point before the part of the irradiation objectirradiated with the first beam spot is solidified.

The present invention discloses a method for manufacturing asemiconductor device wherein the laser beam is scanned on thesemiconductor film along plural straight lines arranging at uniformintervals, wherein a first quasi-linear beam spot formed by scanning thelaser beam along a first straight line among the straight lines overlapspartially a second quasi-linear beam spot formed by scanning the laserbeam along a second straight line adjacent to the first straight line,and wherein the second quasi-linear beam spot is formed by scanning thelaser beam before the part of the semiconductor film irradiated with thefirst quasi-linear beam spot is solidified.

The present invention discloses another method for manufacturing asemiconductor device wherein a laser beam is scanned along a wave-likeline or a saw-like line, wherein when the laser beam is scanned alongthe wave-like line or the saw-like line from a first direction-turningpoint to a third direction-turning point through a seconddirection-turning point, a first beam spot centering on the firstdirection-turning point overlaps partially a second beam spot centeringon the third direction-turning point, and wherein the second beam spotis formed before the part of the semiconductor film irradiated with thefirst beam spot is solidified.

The present invention discloses another method for manufacturing asemiconductor device wherein a laser beam is scanned on thesemiconductor film along a comb-like line, wherein when the laser beamis scanned along the comb-like line from a first angle to a fourth anglethrough second and third angles, a first beam spot centering on thefirst angle overlaps partially a second beam spot centering on thefourth angle, and wherein the second beam spot is formed before the partof the semiconductor film irradiated with the first beam spot issolidified.

By using the laser irradiation apparatus or the method for manufacturinga semiconductor device as described above, the interface between thesolid phase and the liquid phase can be moved in the irradiation objectcontinuously in one direction.

For example, in the case of the continuous wave laser beam, it takesapproximately 100 ns after the semiconductor film is melted by the laserirradiation and before the semiconductor film is solidified completelyaccording to the nonpatent document 1. In this case, the quasi-linearbeam spot may be formed by setting the repetition frequency of the laserbeam to 10 MHz or more. With the above structure, the interface betweenthe solid phase and the liquid phase can be moved continuously in thedirection perpendicular to the major axis of the quasi-linear beam spotwhen before a region in the semiconductor film melted by thequasi-linear beam spot is solidified, the next quasi-linear laser beamis delivered to a region overlapping partially the melted region in thesemiconductor film. Then, as a result of moving the interface betweenthe solid phase and the liquid phase continuously, it is possible toform an aggregation of crystal grains each having a width of 10 to 30 μmin a direction perpendicular to the major axis of the quasi-linear beamspot and a width of 1 to 5 μm in the major-axis direction. By formingthe crystal grain of the single crystal extending long in the directionperpendicular to the major axis of the quasi-linear beam spot, it ispossible to form the TFT having almost no crystal grain boundaries whichintersect the direction where the carrier moves.

[Nonpatent Document 1] Surface Science Vol. 24, No. 6, pp. 375-382, 2003

The upper limit of the pulse repetition frequency of the laser beam inthe uniaxial direction to form the quasi-linear beam spot may bedetermined so that the total energy of the laser beam delivered to anyone point can melt the semiconductor film.

The laser beam used in the present invention is not limited to thecontinuous wave laser beam. For example, the pulsed laser oscillatorwith the repetition frequency of 100 MHz or more, which is extremelyhigher than that used usually (several tens to several hundred Hz), maybe used to perform the laser crystallization. It is said that it takesseveral tens to several hundred ns to solidify the semiconductor filmcompletely after the semiconductor film is irradiated with the pulsedlaser beam. Therefore, by setting the pulse repetition frequency of thelaser beam to several tens to several hundred MHz, before the region inthe semiconductor film melted by the quasi-linear beam spot issolidified, the next quasi-linear beam spot can be delivered to theregion overlapping partially the melted region in the semiconductorfilm. Accordingly, since the interface between the solid phase and theliquid phase can be moved continuously in the semiconductor film, thesemiconductor film having the crystal grain grown continuously in thedirection perpendicular to the major axis of the quasi-linear beam spotcan be formed. Specifically, it is possible to form an aggregation ofcrystal grains each having a width of 10 to 30 μm in a directionperpendicular to the major axis of the quasi-linear beam spot and awidth of 1 to 5 μm in the major-axis direction. By forming the crystalgrain of the single crystal extending long in the directionperpendicular to the major axis of the quasi-linear beam spot, it ispossible to form the TFT having almost no crystal grain boundaries whichintersect the direction where the carrier moves.

When the repetition frequency is extremely high as described above, thepulse width is short consequently to be the order of picosecond orshorter in accordance with the repetition frequency. As a result, anadditional advantage can be obtained in which the interference due tothe reflection at the rear surface of the substrate can be suppressedwhen the laser irradiation is performed vertically to the substrate. Theinterference can be suppressed because the time for which the lightreturned to the semiconductor film after reflecting at the rear surfaceof the 1-mm-thick glass substrate exists simultaneously with the lightincident newly into the semiconductor film can be made extremely shortwhen the pulse width is on the order of picosecond. Usually, the pulsedlaser has a pulse width of ten to several hundred ns for which the lighttravels 3 to 100 m. However, when the pulse repetition frequency isextremely high, the pulse width is on the order of picosecond. Forexample, the light travels approximately 3 mm for a pulse width of 10ps, and this travel distance is much shorter than that when using theconventional pulsed laser. For this reason, the interference can besuppressed more easily between the light returned to the semiconductorfilm after reflecting at the rear surface of the glass substrate and thelight incident newly into the semiconductor film. Therefore, it is notnecessary to irradiate the semiconductor film obliquely in considerationof the interference, and the laser irradiation can be performedvertically to the substrate. This makes the optical design easy, and theenergy distribution of the obtained beam spot can be made morehomogeneous. Moreover, when the laser irradiation is performedobliquely, homogenous laser annealing is difficult because theirradiation condition depends on the scanning direction of theirradiation object. In this case, the laser annealing needs to beperformed only in one direction to perform the homogenous laserannealing despite the decrease in throughput. However, since the laserirradiation can be performed vertically by using the extremely highrepetition frequency, the irradiation condition does not changedepending on the scanning direction. Therefore, the homogeneous laserannealing can be performed even when the irradiation object is scannedso as to move back and forth.

In the case of crystallizing with the use of the conventional pulsedlaser, the impurity such as oxygen, nitrogen, or carbon tends tosegregate in the crystal grain boundary. In particular, when thecrystallization by the laser beam is combined with the crystallizationby the catalyst element, the catalyst element not gettered maysegregate. In the present invention, since the interface between thesolid phase and the liquid phase can be moved continuously, it ispossible to prevent the impurity having positive segregation coefficientfrom segregating, to purify the semiconductor film, and to homogenizethe density of the solute like a zone melting method. Therefore, thecharacteristic of the semiconductor element formed using thesemiconductor film can be enhanced, and the variation of thecharacteristic can be suppressed between the semiconductor elements.

In the present invention, a continuous wave gas or solid-state laser canbe used. The gas laser is, for example, an Ar laser or a Kr laser. Thesolid-state laser is, for example, a YAG laser, a YVO₄ laser, a YLFlaser, a YAlO₃ laser, a Y₂O₃ laser, a glass laser, a ruby laser, analexandrite laser, or a Ti: Sapphire laser.

In the present invention, a pulsed laser oscillator with a repetitionfrequency of 100 MHz or more can be used. When the repetition frequencyof 100 MHz or more is possible, an Ar laser, a Kr laser, an excimerlaser, a CO₂ laser, a YAG laser, a Y₂O₃ laser, a YVO₄ laser, a YLFlaser, a YAlO₃ laser, a glass laser, a ruby laser, an alexandrite laser,a Ti: Sapphire laser, a copper vapor laser, or a gold vapor laser can beused.

The method for manufacturing a semiconductor device of the presentinvention can be applied to the method for manufacturing an integratedcircuit or a semiconductor display device. The semiconductor displaydevice is, for example, a liquid crystal display device, alight-emitting device where a light-emitting element typified by anorganic light-emitting element is equipped in each pixel, a DMD (digitalmnicromirror device), a PDP (plasma display panel), an FED (fieldemission display), and the like.

When the linear beam spot is formed by the conventional method in whichonly the optical system is used, homogenizing the energy distribution inthe beam spot in its major-axis direction is limited. According to thepresent invention, however, the quasi-linear beam spot is formed byscanning the beam spot at high speed in the uniaxial direction so thatthe adjacent beam spots overlap each other. Therefore, the energydistribution of the quasi-linear beam spot in its major-axis directioncan be made more homogeneous without complicating the optical systemcompared with the conventional linear beam spot. Therefore, thecrystallinity of the semiconductor film in the major-axis direction ofthe quasi-linear beam spot can be made more homogeneous, and thevariation of the characteristic between the semiconductor elementsformed using the semiconductor film can be suppressed.

When homogenizing the energy distribution in the major-axis direction islimited according to the conventional method, it is difficult to extendthe linear beam spot longer in the major-axis direction, whichinterrupts the increase of the throughput. In the present invention, thewidth of the quasi-linear beam spot can be extended in the major-axisdirection by increasing the scanning speed of the laser beam in themajor-axis direction while keeping the total energy of the laser beamdelivered to any one point. For this reason, the throughput of the laserirradiation can be increased further without complicating the opticalsystem.

Conventionally, a cylindrical lens has been used as an optical systemfor condensing the laser beam to form a linear beam spot. In the presentinvention, since the beam spot for forming the quasi-linear beam spotmay be circular, the optical system for condensing the laser beam may bea spherical lens. The spherical lens generally has higher accuracy thanthe cylindrical lens, and therefore, the beam spot can have higherenergy density and shorter diameter by the spherical lens. Consequently,in comparison with the conventional linear beam spot, the width of thequasi-linear beam spot in its minor-axis direction can be made shorter,and the width thereof in its major-axis direction can be made longeraccording to the present invention. Thus, the throughput can beincreased further.

Moreover, the crystal grain having large grain size can be formed bymoving the interface between the solid phase and the liquid phasecontinuously in a direction perpendicular to the major axis of thequasi-linear beam spot. Accordingly, at least one island-shapedsemiconductor film can be formed within one crystal grain. Thus, thecarrier is not trapped in the crystal grain boundary, and thesemiconductor device in which the transporting property of the carrierdoes not decrease can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1C are drawings for showing the steps of forming aquasi-linear beam spot by scanning a beam spot in a uniaxial direction;

FIG. 2 is a drawing of an example of a laser irradiation apparatus ofthe present invention;

FIGS. 3A to 3C are drawings for showing the steps of forming aquasi-linear beam spot by a laser beam deflected at an acousto-opticelement;

FIGS. 4A to 4C are drawings for showing the steps of forming aquasi-linear beam spot by scanning a laser beam in a uniaxial direction;

FIG. 5 is a drawing of an example of a laser irradiation apparatus ofthe present invention;

FIGS. 6A to 6C are drawings for showing the step of forming aquasi-linear beam spot by a laser beam deflected at a polygon mirror;

FIGS. 7A to 7C are drawings for showing a manufacturing method of asemiconductor device of the present invention;

FIGS. 8A to 8D are drawings for showing a manufacturing method of asemiconductor device of the present invention;

FIGS. 9A to 9D are drawings for showing a manufacturing method of asemiconductor device of the present invention;

FIG. 10 is a drawing for showing a configuration of the pixel in alight-emitting device, which is one of semiconductor devices formed bythe laser irradiation apparatus of the present invention;

FIGS. 11A to 11C are drawings for showing the step of forming aquasi-linear beam spot by scanning a beam spot in a uniaxial direction;

FIGS. 12A to 12C are drawings for showing the step of forming aquasi-linear beam spot by scanning a beam spot in a uniaxial direction;

FIG. 13 is a drawing for showing an example of a laser irradiationapparatus of the present invention; and

FIGS. 14A to 14E are drawings for showing the step of forming aquasi-linear beam spot by scanning the beam spot in a uniaxialdirection.

DETAILED DESCRIPTION OF THE INVENTION Embodiment Mode

Embodiment modes and embodiments are hereinafter described withreference to drawings. However, since the present invention can beembodied in many different modes, it is easily understood by those whoare skilled in the art that the mode and the detail of the presentinvention can be changed and modified within the content and the scopeof the present invention. Therefore, the present invention is notlimited to the description of the embodiment modes and the embodiments.Moreover, the shape of the beam spot in the following embodiment modesand embodiments is not limited to circular, and it may be elliptical orrectangular.

Embodiment Mode 1

A step of forming a quasi-linear beam spot used in the present inventionis described with reference to FIGS. 1A to 1C. As shown in FIG. 1A, aquasi-linear beam spot 100 is formed by scanning a beam spot 101 of thelaser beam in a uniaxial direction or along a straight line as indicatedby a solid-line arrow.

In FIG. 1A, the quasi-linear beam spot 100 is formed by scanning thebeam spot 101 so as to move it back and forth. However, the presentinvention is not limited to this configuration, and the quasi-linearbeam spot 100 may be formed by scanning the beam spot 101 in only onedirection. Moreover, FIG. 1A illustrates the quasi-linear beam spot 100formed in such a way that after the beam spot 101 is scanned from leftto right, it is scanned from right to left again. However, the presentinvention is not limited to this configuration. In the presentinvention, the beam spot 101 may be scanned at least once in any onepoint in the quasi-linear beam spot 100.

In the case of using the semiconductor film as the irradiation object,the scanning speed of the beam spot 101 is set so that before any onepoint in the semiconductor film melted by the laser beam is solidifiedcompletely, the one point is irradiated again with the next laser beam.In the case of FIG. 1A, when the laser beam is scanned from right toleft, the scanning speed of the beam spot 101 is set so that before theright end of the quasi-linear beam spot 100 in the uniaxial directionmelted by the beam spot 101 is solidified, the beam spot 101 is scannedto the left end thereof in the uniaxial direction. Thus, thequasi-linear beam spot can keep the irradiation object melted for acertain period.

In the case of forming the quasi-linear beam spot by the pulsed laserbeam, the pulsed laser beam is scanned so that the adjacent pulsed beamspots overlap each other.

The scanning speed of the laser beam in the uniaxial direction is set sothat the total energy of the laser beam delivered to any one point canmelt the semiconductor film.

Although the present embodiment mode has described an example of formingthe quasi-linear beam spot 100 by scanning the beam spot 101 only in theuniaxial direction, the present invention is not limited to thisconfiguration. The beam spot 101 may be scanned in two or moredirections when the quasi-linear beam spot 100 can be formed in the end.

In the present invention, the quasi-linear beam spot 100 is scannedfurther in a direction perpendicular to the uniaxial direction, which isthe direction perpendicular to the major axis of the quasi-linear beamspot 100. FIG. 1B shows the step of forming a quasi-linear beam spot 103by scanning the quasi-linear beam spot 100 shown in FIG. 1A in adirection indicated by a dotted-line arrow, which is perpendicular tothe major axis of the quasi-linear beam spot 100.

Within the quasi-linear beam spot 100, the semiconductor film is not ina completely melted state. Therefore, the interface between the solidphase and the liquid phase can be moved continuously by irradiating thesemiconductor film with the quasi-linear beam spot 103 which partiallyoverlaps the quasi-linear beam spot 100 before the semiconductor filmirradiated with the quasi-linear beam spot 100 is solidified.

FIG. 1C illustrates the step of crystallizing the semiconductor film byrepeating the above operation. In FIG. 1C, the semiconductor film 102,which is the irradiation object, is crystallized by scanning the beamspot 101 along plural straight lines arranging at uniform intervals asindicated by an arrow. In this case, the quasi-linear beam spot 100,which is formed by scanning the laser beam along a straight line, andthe quasi-linear beam spot 103, which is formed by scanning the laserbeam along the next straight line, are scanned so that they partiallyoverlap as shown in FIG. 1B. This can form a crystal grain of a singlecrystal extending long in the scanning direction indicated by thedotted-line arrow. Specifically, the quasi-linear beam spot 100 and thequasi-linear beam spot 103 overlap in such a way that regions in thesebeam spots along their major axes overlap each other.

The scanning speed of the laser beam is set so that before a part of theirradiation object irradiated with the quasi-linear beam spot 100 issolidified, the quasi-linear beam spot 103 can be formed. Morespecifically, the laser irradiation is performed in such a way thatbefore a region of the irradiation object melted by any one of pluralbeam spots constituting the quasi-linear beam spot 100 is solidified,one of plural beam spots constituting the quasi-linear beam spot 103 isdelivered so as to overlap the melted region. Thus, the crystal grain inthe irradiation object can be grown continuously in one direction, and alarge crystal grain can be formed.

It takes approximately 100 ns to solidify silicon after being irradiatedwith the laser beam. Therefore, when the irradiation object is siliconin this embodiment mode, the quasi-linear beam spot 103 may be formedwithin 100 ns after the quasi-linear beam spot 100 begins to be formed.

Next, a configuration of the laser irradiation apparatus of the presentinvention is described. FIG. 2 shows an example of the laser irradiationapparatus of the present invention. The laser irradiation apparatusillustrated in FIG. 2 includes a laser oscillator 201, a condensingoptical system 202, a mirror 203, an acousto-optic element 204, an fθlens 205, a stage 206, an X-axis direction position controlling means209, and a Y-axis direction position controlling means 210.

The laser oscillator 201 is, for example, a continuous wave laseroscillator or a pulsed laser oscillator with a repetition frequency of100 MHz or more. In this embodiment mode, the laser oscillator 201 is acontinuous wave YVO₄ laser providing 10 W and emitting a laser beamwhose cross section is circular and has a diameter of 1 mm.

The laser beam emitted from the laser oscillator 201 is incident intothe condensing optical system 202. The condensing optical system 202 maybe any kind of optical system which can condense the laser beam, and itmay be, for example, a spherical lens or a Flesnel lens. In thisembodiment mode, the laser beam having the circular cross section isreduced in size from a diameter of 1 mm to a diameter of 0.1 mm by thecondensing optical system 202. The laser beam condensed by thecondensing optical system 202 is reflected on the mirror 203 andincident into the acousto-optic element 204.

When an acoustic wave such as a supersonic wave, which has highfrequency, is applied to the acousto-optic element 204, the refractiveindex of the acousto-optic element 204 is modulated periodically.Therefore, the laser beam incident into the acousto-optic element 204can be deflected with high frequency on the order of gigahertz. The beamspot can be scanned repeatedly with high frequency in the uniaxialdirection by using the acousto-optic element 204. Although thisembodiment mode uses the acousto-optic element as the optical system forscanning the beam spot repeatedly in the uniaxial direction, the presentinvention is not limited to this configuration. The optical system suchas a polygon mirror or a resonant scanner, which can scan the beam spotrepeatedly with high frequency in the uniaxial direction, can be used.

The laser beam deflected by the acousto-optic element 204 is incidentinto the fθ lens 205. The deflected laser beam is condensed by the fθlens 205 so that the laser beam is always focused on the irradiationobject. The stage 206 can have the irradiation object mounted thereover.FIG. 2 shows an example in which the irradiation object is asemiconductor film 208 formed over a substrate 207. With the fθ lens 205for focusing the laser beam on the semiconductor film 208 mounted overthe stage 206, the beam spot scanned periodically in the uniaxialdirection can be formed. A trajectory of the beam spot scannedperiodically in the uniaxial direction is illustrated as a quasi-linearbeam spot 211 in FIG. 2.

With reference to FIGS. 3A to 3C, the step of forming the quasi-linearbeam spot 211 by the laser beam deflected at the acousto-optic element204 is described. In FIGS. 3A to 3C, the laser beam deflected by theacousto-optic element 204 and the fθ lens 205 shown in FIG. 2 is scannedon the semiconductor film 208. As shown in FIGS. 3A to 3C, after thelaser beam indicated by the solid-line arrow is deflected by theacousto-optic element 204, the laser beam is condensed by the fθ lens205, and the laser beam is focused on the semiconductor film 208.

Then, when the refractive index of the acousto-optic element 204 ismodulated in order of FIGS. 3A, 3B, and 3C, the laser beam is deflectedin a direction indicated by a white arrow. With the deflection of thelaser beam, the region on the semiconductor film 208 where the laserbeam is focused, which is the beam spot, is scanned in the uniaxialdirection.

Since it is necessary that the semiconductor film 208 is not solidifiedcompletely within the quasi-linear beam spot 211, the beam spot needs tobe scanned in uniaxial direction at the speed satisfying the abovecondition. In the case of the laser irradiation apparatus shown in FIG.2, the scanning speed of the beam spot in the uniaxial direction can becontrolled by the frequency of the acoustic wave applied to theacousto-optic element 204.

In this embodiment mode, the refractive index of the acousto-opticelement 204 is modulated with the frequency of 80 MHz. In thisembodiment mode, the beam spot formed on the semiconductor film 208 bythe fθ lens 205 has a diameter of 5 μm. When the quasi-linear beam spot211 is formed under the above condition, the quasi-linear beam spot 211has a width of 5 μm in its minor-axis direction and a width ofapproximately 400 μm in the uniaxial direction or the major-axisdirection.

In the laser irradiation apparatus shown in FIG. 2, the quasi-linearbeam spot 211 can be scanned in a direction perpendicular to theuniaxial direction (a direction perpendicular to the major axis of thequasi-linear beam spot) by the X-axis direction position controllingmeans 209 which can move the stage 206 in the X-axis direction. That isto say, the position of the irradiation object relative to the laserbeam can be moved in a direction indicated by a dotted-line arrow inFIG. 1C. The speed of moving the X-axis direction position controllingmeans 209 is much lower than the scanning speed of the beam spot 101 inthe uniaxial direction. This can achieve the scanning shown in FIG. 1C.The X-axis direction position controlling means 209 moves the stage 206at the constant speed in a direction perpendicular to the major axis ofthe quasi-linear beam spot. Moreover, the laser irradiation apparatusshown in FIG. 2 includes the Y-axis direction position controlling means210 which can move the stage 206 in a Y-axis direction perpendicular tothe X-axis direction.

Although the two position controlling means of the X-axis directionposition controlling means 209 and the Y-axis direction positioncontrolling means 210 are used in FIG. 2 to control the position of thequasi-linear beam spot 211 relative to the stage 206, the presentinvention is not limited to this configuration. The laser irradiationapparatus of the present invention may have at least the X-axisdirection position controlling means 209. In addition to the X-axisdirection position controlling means 209, another position controllingmeans may be provided which can rotate the stage 206 in the planeincluding the stage 206.

In this embodiment mode, the semiconductor film 208 is crystallized byscanning the laser beam along plural straight lines arranging at uniformintervals as shown in FIG. 1C with the use of the acousto-optic element204 and at least the X-axis direction position controlling means 209.

In this embodiment mode, the stage 206 is scanned in the X-axisdirection at a speed of 100 mm/s or more by the X-axis directionposition controlling means 209. When the whole surface of thesemiconductor film 208 is irradiated with the laser beam, the laserirradiation may be performed in the following way. After scanning thequasi-linear beam spot 211 in the major-axis direction by the Y-axisdirection position controlling means 210, the quasi-linear beam spot 211is scanned in the X-axis direction by the X-axis direction positioncontrolling means 209 again, and this operation is performed repeatedly.Moreover, the position of the quasi-linear beam spot 211 relative to thestage 206 may be controlled by moving the optical system itself. In sucha case, the stage does not need to move, and the optical system denotedwith the reference numerals 201 to 205 in FIG. 2 may be moved in bothX-axis direction and Y-axis direction.

When the laser oscillator 201 is the pulsed laser oscillator, the lengthof the quasi-linear beam spot 211 in the major-axis direction is limitedby the repetition frequency of the pulse oscillation. Consequently, itis necessary to design the quasi-linear beam spot 211 in considerationof the repetition frequency of the pulse oscillation. Specifically, thepulse repetition frequency F [MHz] may satisfy the following inequality1 where d is the length [μm] of the beam spot in the uniaxial direction,L is the width [μm] of the quasi-linear beam spot 211 in the uniaxialdirection, and f is the frequency [MHz] of the deflection by theacousto-optic element 204.F≧2Lf/d  [Inequality 1]

For example, when the beam spot has a length d of 10 μm in the uniaxialdirection, the quasi-linear beam spot 211 has a width L of 200 μm in theuniaxial direction, and the frequency f of the deflection by theacousto-optic element 204 is 10 MHz, it is understood from theinequality 1 that the pulse repetition frequency F may be 400 MHz ormore.

In the laser irradiation apparatus shown in FIG. 2, the condensingoptical system 202 is not always necessary. However, by using thecondensing optical system 202, a smaller acousto-optic element can beused because the size of the cross section of the laser beam incidentinto the acousto-optic element 204 can be suppressed. Moreover, theoptical system such as a mirror 203 which deflects the optical path ofthe laser beam is not always necessary, and it may be providedappropriately as needed. Furthermore, the fθ lens 205 is not alwaysnecessary. However, by using the fθ lens 205, the speed and the size ofthe beam spot scanned in the uniaxial direction within the quasi-linearbeam spot 211 can be made constant.

The optical system used in the laser irradiation apparatus of thepresent invention is not limited to that shown in FIG. 2, and anotheroptical system may be added appropriately by the designer.

Embodiment Mode 2

With reference to FIGS. 11A to 11C, this embodiment mode describes ascanning method of the laser beam which is different from the scanningmethod shown in the embodiment mode 1. Other parts of this embodimentmode except the scanning method of the laser beam are the same as thosein the embodiment mode 1. The laser irradiation apparatus shown in FIG.2 is used in this embodiment mode.

In FIGS. 11A to 11C, reference numerals 1101 and 1102 denotequasi-linear beam spots, reference numerals 1103 and 1104 denote beamspots, and a reference numeral 1105 denotes a semiconductor film, whichis the irradiation object. By scanning the beam spot shown in FIGS. 11Ato 11C, the quasi-linear beam spot is formed in the same way as theembodiment mode 1. The quasi-linear beam spot 1101 and the quasi-linearbeam spot 1102, which is formed sequentially after the quasi-linear beamspot 1101, are scanned so that regions in these beam spots parallel totheir major axes overlap each other.

The laser beam is scanned along a saw-like line in FIG. 11A, along awave-like line in FIG. 11B, and along a comb-like line in FIG. 11C. Whenthe laser beam is scanned along the saw-like line or the wave-like lineas shown in FIGS. 11A and 11B, the opposite end portions of thequasi-linear beam spot are hereinafter referred to as direction-turningpoints. In the case of partially overlapping the quasi-linear beam spots1101 and 1102 in FIGS. 11A and 11B, the quasi-linear beam spots 1101 and1102 overlap partially automatically by overlapping the beam spot 1103centering on a certain direction-turning point and the beam spot 1104centering on the direction-turning point after the nextdirection-turning point. In FIG. 11B, the arrow is not at thedirection-turning point on the wave-like line but is just before thedirection-turning point. However, actually, the quasi-linear beam spotis formed by moving the laser beam back and forth on the wave-like linebetween the direction-turning point and the next direction-turningpoint.

FIG. 11C is a scanning method in which the scanning method shown in FIG.1C of the embodiment mode 1 is modified. In FIG. 1C, after forming thequasi-linear beam spot 100, the beam spot 101 is not scanned on theirradiation object until the quasi-linear beam spot 103 is formed.Meanwhile, FIG. 11C shows an example of keeping the laser irradiation tothe irradiation object even after forming the quasi-linear beam spot1101 and before forming the quasi-linear beam 1102. To homogenize theenergy density distribution of the laser beam delivered to thesemiconductor film 1105 by the scanning method shown in FIG. 11C, thescanning speed is increased or the output of the laser beam is loweredat the opposite ends of the quasi-linear beam spot. Thus, the totalenergy of the laser beam absorbed in the opposite ends of thequasi-linear beam spot can be made substantially the same as that in theregion irradiated with other beam spots.

In the case of the scanning methods shown in FIGS. 11A and 11B, thelaser beam is scanned at least once from the direction-turning point,which is the center of the beam spot 1103, to the direction-turningpoint, which is the center of the beam spot 1104, through onedirection-turning point. For this reason, in order to grow the crystalgrain continuously in a direction perpendicular to the major axis of thequasi-linear beam spot, the laser beam may be scanned up to the positionof the beam spot 1104 in the figure before a part of the semiconductorfilm 1105 irradiated with the beam spot 1103 is solidified. Then,accordingly, the quasi-linear beam spot 1102 can be formed before a partof the irradiation object irradiated with the quasi-linear beam spot1101 is solidified, and the interface between the solid phase and theliquid phase can be moved in a direction perpendicular to the major axisof the quasi-linear beam spot. Thus, a large crystal grain can beformed.

In FIG. 11C, the laser beam is scanned from the first angle of thecomb-like line, which is the center of the beam spot 1103, to the fourthangle thereof, which is the center of the beam spot 1104, through thesecond and third angles. Therefore, in order to grow continuously thecrystal grain in a direction perpendicular to the major axis of thequasi-linear beam spot, the laser beam may be scanned up to the positionof the beam spot 1104 in the figure before a part of the semiconductorfilm 1105 irradiated with the beam spot 1103 is solidified. As a result,the quasi-linear beam spot 1102 can be formed before a part of theirradiation object irradiated with the quasi-linear beam spot 1101 issolidified, and the interface between the solid phase and the liquidphase can be moved in a direction perpendicular to the major axis of thequasi-linear beam spot. Thus, the large crystal grain can be formed.

In the quasi-linear beam spot 1101, the beam spot 1103 is delivered tothe irradiation object first. Meanwhile, in the quasi-linear beam spot1102, the beam spot 1104 is delivered to the irradiation object last.Consequently, in order to grow the crystal grain continuously in adirection perpendicular to the major axis of the quasi-linear beam spot,the laser beam may be scanned to the position of the beam spot 1104 inthe figure before a part of the semiconductor film 1105 irradiated withthe beam spot 1103 is solidified. Then, accordingly, the quasi-linearbeam spot 1102 can be formed before a part of the irradiation objectirradiated with the quasi-linear beam spot 1101 is solidified, and theinterface between the solid phase and the liquid phase can be moved in adirection perpendicular to the major axis of the quasi-linear beam spot.Thus, a large crystal grain can be formed.

The scanning methods shown in FIGS. 11A to 11C can be achieved by movingboth the acousto-optic element 204 and the X-axis direction positioncontrolling means 209 in FIG. 2 in a timely manner. The acousto-opticelement 204 deflects the laser beam at a certain frequency. By movingthe X-axis direction position controlling means in accordance with thecertain frequency of the acousto-optic element 204, various scanningmethods shown in FIGS. 11A to 11C are achieved. In the scanning methodsshown in FIGS. 11A and 11B, the stage is moved by the X-axis directionposition controlling means while scanning the laser beam by theacousto-optic element. Moreover, in the scanning method shown in FIG.11C, the stage is moved by the X-axis direction position controllingmeans while scanning the laser beam by the acousto-optic element. In thescanning method of FIG. 11C, the stage is moved by the X-axis directionposition controlling means when the laser beam is at the end portion ofthe quasi-linear beam spot.

Embodiment Mode 3

Another embodiment mode of the present invention is described.

First, the step of forming a quasi-linear beam spot used in the presentinvention is described with reference to FIGS. 4A to 4C. FIG. 4A shows aquasi-linear beam spot 300 formed by scanning a beam spot 301 of a laserbeam in one direction or along a straight line as indicated by asolid-line arrow.

In FIG. 4A, unlike the embodiment mode 1, the beam spot 301 is scannedonly in one direction to form the quasi-linear beam spot 300. The totaltime of laser irradiation can be homogenized in any one point within thequasi-linear beam spot 300 by scanning the beam spot 301 only in onedirection as shown in FIG. 4A. Although FIG. 4A illustrates the beamspot 301 scanned from left to right, the present invention is notlimited to this configuration. In the present invention, the beam spot301 may be scanned at least once in any one point within thequasi-linear beam spot 300.

In the case of FIG. 4A, the scanning speed of the beam spot 301 may beset so that before the region at the left edge in a uniaxial direction,which is melted by the beam spot 301, is solidified, the beam spot 301is scanned to the right edge in the uniaxial direction within thequasi-linear beam spot 300.

In this embodiment mode, in the same way as the embodiment mode 1, thescanning speed of the laser beam in the one direction is set so that thetotal energy of the laser beam delivered to any one point can melt thesemiconductor film.

Although this embodiment mode showed the example of forming thequasi-linear beam spot 300 by scanning the beam spot 301 only in the onedirection, the present invention is not limited to this configuration.The beam spot may be scanned in two or more directions when thequasi-linear beam spot 300 is formed in the end.

The quasi-linear beam spot 300 is scanned further in the directionperpendicular to the one direction, which is the direction perpendicularto the major axis of the quasi-linear beam spot 300. FIG. 4B shows thestep of forming the quasi-linear beam spot 303 by scanning thequasi-linear beam spot 300 shown in FIG. 4A in the directionperpendicular to the major axis of the quasi-linear beam spot 300 asindicated by a dotted-line arrow.

Within the quasi-linear beam spot 300, the semiconductor film is notsolidified completely but is still melted. Therefore, the interfacebetween the solid phase and the liquid phase can be moved continuouslyin the semiconductor film by irradiating the semiconductor film with thequasi-linear beam spot 303 before a part of the semiconductor filmirradiated with the quasi-linear beam spot 300 is solidified. At thistime, the quasi-linear beam spots 300 and 303 partially overlap eachother.

FIG. 4C and FIGS. 12A to 12C show the step of crystallizing thesemiconductor film by repeating the above operation. The semiconductorfilm 302, which is the irradiation object, is crystallized by the laserbeam while scanning the beam spot 301 along plural straight linesarranging at uniform intervals. In this case, as shown in FIG. 4B, thequasi-linear beam spot 300 partially overlaps the quasi-linear beam spot303 formed sequentially, and the quasi-linear beam spot 303 is formedbefore the part of the irradiation object irradiated with thequasi-linear beam spot 300 is solidified. Thus, a crystal grain of asingle crystal extending long in the scanning direction indicated by anarrow can be formed. Specifically, the adjacent quasi-linear beam spotsoverlap in such a way that regions in these beam spots along their majoraxes overlap each other. Moreover, in the case of using silicon as theirradiation object, since it takes approximately 100 ns to solidifysilicon, the quasi-linear beam spot 303 is formed within 100 ns afterthe quasi-linear beam spot 300 begins to be formed.

FIGS. 12A to 12C show various scanning methods of the laser beam. Thelaser beam is scanned along a saw-like line or a zigzag line in FIG.12A, a wave-like line in FIG. 12B, and a comb-like line in FIG. 12C. Inthe same way as FIG. 4C, the quasi-linear beam spot 1201 partiallyoverlaps the next quasi-linear beam spot 1202, and the quasi-linear beamspot 1202 is formed before the part of the irradiation object irradiatedwith the quasi-linear beam spot 1201 is solidified.

In the scanning methods shown in FIGS. 12A and 12B, the quasi-linearbeam spots 1201 and 1202 partially overlap automatically when they areformed in such a way that the beam spot 1203 centering on a certaindirection-turning point overlaps partially the beam spot 1204 centeringon the direction-turning point after the next direction-turning point.

FIG. 12C is a modification of FIG. 4C and shows an example of keepingthe laser irradiation to the irradiation object even after forming thequasi-linear beam spot 1201 and before forming the quasi-linear beamspot 1202. To homogenize the energy density distribution of the laserbeam delivered to the semiconductor film 1205 by the scanning methodshown in FIG. 12C, the scanning speed is increased or the output powerof the laser beam is lowered at the opposite ends of the quasi-linearbeam spot. Thus, the laser energy absorbed in the opposite ends of thequasi-linear beam spot can be made almost the same as that in otherirradiated regions.

Moreover, in the quasi-linear beam spot 1201, the beam spot 1203 isdelivered to the irradiation object first. Meanwhile, in thequasi-linear beam spot 1202, the beam spot 1204 is delivered to theirradiation object last. Specifically, in FIGS. 12A and 12B, the laserbeam is scanned from the direction-turning point, which is the center ofthe beam spot 1203, to another direction-turning point, which is thecenter of the beam spot 1204, through another direction-turning point.In the case of FIG. 12C, the laser beam is scanned along the comb-likeline from one angle, which is the center of the beam spot 1203, toanother angle, which is the center of the beam spot 1204, throughanother two angles. Therefore, in order to grow the crystal graincontinuously in a direction perpendicular to the major axis of thequasi-linear beam spot, the laser beam may be scanned to the position ofthe beam spot 1204 in the figure before the part of the semiconductorfilm 1205 irradiated with the beam spot 1203 is solidified. As a result,the quasi-linear beam spot 1202 is formed before the part of theirradiation object irradiated with the quasi-linear beam spot 1201 issolidified, and the crystal having large grain size can be formed.

It takes approximately 100 ns to solidify silicon after being irradiatedwith the laser beam. Therefore, when the semiconductor film 1205, whichis the irradiation object, is silicon, the laser beam may be scanned tothe position of the beam spot 1204 in the figure within 100 ns after thebeam spot 1203 is delivered to the semiconductor film 1205.

Next, a configuration of the laser irradiation apparatus in thisembodiment mode is described. FIG. 5 shows an example of the laserirradiation apparatus of this embodiment mode. The laser irradiationapparatus shown in FIG. 5 includes a laser oscillator 401, a condensingoptical system 402, a polygon mirror 403, an fθ lens 404, a stage 405,an X-axis direction position controlling means 408, and a Y-axisdirection position controlling means 409.

The laser oscillator 401 can be, for example, a continuous wave laseroscillator or a pulsed laser oscillator with a repetition frequency of100 MHz or more in the same way as the embodiment mode 1. A laser beamemitted from the laser oscillator 401 is incident into the condensingoptical system 402. The condensing optical system 402 may be any opticalsystem when it can condense the laser beam, and it may be, for example,a spherical lens or a Flesnel lens. The laser beam condensed by thecondensing optical system 402 is incident into the polygon mirror 403.

The polygon mirror 403 is a rotator having a series of flat reflectingplanes provided continuously therearound. When the laser beam isincident into the polygon mirror 403, the polygon mirror 403 can deflectthe laser beam repeatedly in the same direction. By using the polygonmirror 403, the beam spot can be scanned repeatedly in a uniaxialdirection at high frequency.

The laser beam deflected by the polygon mirror 403 is incident into thefθ lens 404. The fθ lens 404 can condense the deflected laser beam so asto focus it on the irradiation object constantly. The stage 405 can havethe irradiation object mounted thereover. In FIG. 5, the irradiationobject is a semiconductor film 407 formed over a substrate 406. Aquasi-linear beam spot scanned periodically in the uniaxial directioncan be formed when the fθ lens 404 focuses the laser beam on thesemiconductor film 407 mounted over the stage 405. The trajectory of thebeam spot scanned periodically in the uniaxial direction is illustratedas a quasi-linear beam spot 410 in FIG. 5.

FIG. 6 illustrates the step of forming the quasi-linear beam spot 410 bythe laser beam deflected by the polygon mirror 403. FIGS. 6A to 6C arethe drawings in which the laser beam deflected by the polygon mirror 403and the fθ lens 404 is scanned on the semiconductor film 407. As shownin FIGS. 6A to 6C, after the polygon mirror 403 deflects the laser beamillustrated with the solid-line, the fθ lens 404 condenses the laserbeam to focus it on the semiconductor film 407.

When the polygon mirror 403 is rotated in the order of FIGS. 6A, 6B, and6C, the angle of a reflecting plane 411 of the polygon mirror 403changes to deflect the laser beam in a direction indicated by a whitearrow. With the deflection of the laser beam, a region on which thelaser beam is focused, which is the beam spot, is moved in the uniaxialdirection. When the polygon mirror 403 is rotated, the laser beam isdeflected by the next reflecting plane adjacent to the reflecting plane411, and therefore, the beam spot can be scanned repeatedly in the samedirection.

Since a part of the semiconductor film 407 within the quasi-linear beamspot 410 needs not to be completely solidified, it is necessary to scanthe beam spot in the uniaxial direction at the speed satisfying theabove condition. In the case of the laser irradiation apparatus shown inFIG. 5, the scanning speed of the beam spot in the uniaxial directioncan be controlled by the frequency of rotating the polygon mirror 403.Moreover, the length of the quasi-linear beam spot 410 in its major-axisdirection can be controlled by the width of the reflecting plane 411 ofthe polygon mirror 403 in its rotating direction.

Furthermore, in the laser irradiation apparatus shown in FIG. 5, thequasi-linear beam spot 410 can be scanned in a direction perpendicularto the uniaxial direction (a direction perpendicular to the major axisof the quasi-linear beam spot) by the X-axis direction positioncontrolling means 408 which can move the position of the stage 405 inthe X-axis direction. The X-axis direction position controlling means408 moves the stage 405 much more slowly in the X-axis direction than inthe uniaxial direction where the laser beam is scanned. By such anoperation, the scanning shown in FIG. 4C can be achieved. The X-axisdirection position controlling means 408 moves the stage 405 at theconstant speed in the direction perpendicular to the major axis of thequasi-linear beam spot. Thus, the crystal having the large grain sizecan be formed. Moreover, by moving the stage in the X-axis directioneven while forming the quasi-linear beam spot, the scanning shown inFIGS. 12B and 12C are achieved. The laser irradiation apparatus shown inFIG. 5 has the Y-axis direction position controlling means 409 which canmove the stage 405 in the Y-axis direction perpendicular to the X-axisdirection.

Although the position of the quasi-linear beam spot 410 relative to thestage 405 is controlled by the X-axis direction position controllingmeans 408 and the Y-axis direction position controlling means 409 inFIG. 5, the present invention is not limited to this configuration. Thelaser irradiation apparatus of the present invention may have at leastthe X-axis direction position controlling means 408. In addition to theX-axis direction position controlling means 408, a position controllingmeans which can control the stage 405 in the plane including the stage405 may be provided.

When the whole surface of the semiconductor film 407 is irradiated withthe laser beam, the laser irradiation may be performed in the followingway. After scanning the quasi-linear beam spot 410 in the X-axisdirection by the X-axis direction position controlling means 408, thequasi-linear beam spot 410 is scanned in its major-axis direction by theY-axis direction position controlling means 409, and this operation isperformed repeatedly. The position of the quasi-linear beam spot 410relative to the stage 405 may be controlled by moving the optical systemitself. In such a case, the stage does not need to be moved, and theoptical systems denoted with reference numerals 401 to 405 may be movedin both X-axis direction and Y-axis direction.

When the laser oscillator 401 is a pulsed laser oscillator, the lengthof the quasi-linear beam spot 410 in its major-axis direction is limitedby the repetition frequency of the pulsed laser oscillator. Therefore,it is necessary to design the quasi-linear beam spot 410 inconsideration of the repetition frequency of the pulse oscillation.Specifically, in the same way as the embodiment mode 1, the repetitionfrequency of the pulse oscillation may satisfy the inequality 1described above. In the inequality 1, f is the frequency of the rotationof the polygon mirror in this embodiment mode though f is the frequencyof the deflection of the acousto-optic element 204 in the embodimentmode 1.

The laser irradiation apparatus shown in FIG. 5 does not always requirethe condensing optical system 402. However, with the condensing opticalsystem 402, the quasi-linear beam spot 410 can have shorter width in theminor-axis direction and longer width in the major-axis direction, andthe throughput can be increased accordingly. The optical system such asa mirror which can change the optical path of the laser beam is notalways necessary, and it may be provided appropriately as needed.Moreover, the fθ lens 404 is not always necessary. However, by using thefθ lens 404, the speed and the size of the beam spot scanned in auniaxial direction in the quasi-linear beam spot 410 can be madeconstant.

The optical system used in the laser irradiation apparatus of thepresent invention is not limited to that shown in FIG. 5, and a designercan add other optical system appropriately as needed.

The present embodiment mode can be freely combined with the embodimentmode 1 or 2 within the possible range.

Embodiment Mode 4

The embodiment modes 1 to 3 have described the example in which thelaser irradiation is performed to the irradiation objecttwo-dimensionally by scanning the laser beam along a straight line withthe use of the optical system and moving the stage in a directionperpendicular to the scanning direction of the laser beam. Thisembodiment mode describes an example in which the laser irradiation isperformed to the irradiation object two-dimensionally only by theoptical system without using the means for moving the stage.

FIG. 13 shows a laser irradiation apparatus of this embodiment mode. Thelaser irradiation apparatus includes a laser oscillator 1301, acondensing optical system 1302, a first deflecting optical system 1311,a second deflecting optical system 1303, and an fθ lens 1304. Each ofthe first and second deflecting optical systems may be any opticalsystem when it can scan the laser beam repeatedly in the uniaxialdirection at high frequency. For example, a polygon mirror, a resonantscanner, or an acousto-optic element may be used. In FIG. 13, the firstdeflecting optical system 1311 is the acousto-optic element, and thesecond deflecting optical system 1303 is the polygon mirror. A referencenumeral 1305 denotes a stage, and a substrate 1306 with a semiconductorfilm 1307 formed thereover can be mounted over the stage 1305.

The laser beam can be scanned in the uniaxial direction and thedirection perpendicular to the uniaxial direction by using the first andsecond deflecting optical systems 1311 and 1303 in combination. First,the laser beam is scanned in the uniaxial direction by the firstdeflecting optical system. The second deflecting optical system 1303 isprovided so as to deflect the laser beam, which has been alreadydeflected by the first deflecting optical system 1311, further in thedirection perpendicular to the uniaxial direction. The beam spot 1310formed thus is larger than the quasi-linear beam spot formed by only onedeflecting optical system.

When the laser beam is scanned by a width of M in the uniaxial directionwith the first deflecting optical system and by a width of N in thedirection perpendicular to the uniaxial direction with the seconddeflecting optical system, the rectangular beam spot 1310 having thesides with lengths of M and N can be formed.

Various scanning methods are possible to form the beam spot 1310. FIG.14A is a top view for showing the beam spot 1310 formed on thesemiconductor film 1307. Each of FIGS. 14B to 14E shows an example of ascanning method of the laser beam to form the beam spot 1310. Thesescanning methods are the same as those shown in the embodiment modes 1to 3. The laser beam is scanned along plural straight lines arranging atuniform intervals in FIG. 14B, along a saw-like line or a zigzag line inFIG. 14C, along a wave-like line in FIG. 14D, and along a comb-like linein FIG. 14E. In this embodiment mode, the laser beam is scannedtwo-dimensionally by using the first and second deflecting opticalsystems in combination. By controlling these two deflecting opticalsystems appropriately, the laser beam can be scanned in various ways inaddition to those shown in FIGS. 14B to 14E. The quasi-linear beam spot1401 and the next quasi-linear beam spot 1402 are formed in the same wayas the embodiment modes 1 and 2. Specifically, the quasi-linear beamspots 1401 and 1402 partially overlap, and the quasi-linear beam spot1402 is formed before a part of the irradiation object irradiated withthe quasi-linear beam spot 1401 is solidified. Thus, the crystal can begrown in the direction perpendicular to the major axis of thequasi-linear beam spot in the beam spot 1310, and the crystal having thelarge grain size can be obtained.

When one of the first and second deflecting optical systems is used,only a part of the semiconductor film 1307 can be crystallized.Therefore, an X-axis direction position controlling means 1308 and aY-axis direction position controlling means 1309 may be used to move theirradiation object so as to crystallize the whole surface of thesemiconductor film. Alternatively, the optical systems denoted withreference numerals 1301 to 1304 and 1311 may be moved instead of theirradiation object to irradiate the whole surface of the semiconductorfilm.

In this embodiment mode, a part of the semiconductor film within therange of the beam spot 1310 can be crystallized surely without using theX-axis and Y-axis direction position controlling means. Moreover, acrystalline semiconductor film in which the crystal grain is grown inone direction can be obtained. Therefore, this embodiment mode issuitable for the manufacturing method in which after forming a pluralityof semiconductor elements over a substrate, they are divided intoindividual semiconductor elements with which plural ID chips aremanufactured.

The laser irradiation apparatus shown in FIG. 13 does not always requirethe condensing optical system 1302. However, since the condensingoptical system 1302 can suppress the divergence of the cross section ofthe laser beam incident into the first deflecting optical system 1311,the first deflecting optical system 1311 can be made smaller. Moreover,the fθ lens 1304 is not always necessary. However, by using the fθ lens1304, the speed or the size of the laser beam scanned within the beamspot 1310 can be made constant.

The optical system used in the laser irradiation apparatus of thepresent invention is not limited to that shown in FIG. 13, and adesigner can add an appropriate optical system as needed.

This embodiment mode may be freely combined with any one of theembodiment modes 1 to 3.

Embodiment 1

Next, a method for manufacturing a semiconductor device of the presentinvention is described with reference to FIGS. 7A to 7C.

As shown in FIG. 7A, a base film 501 is formed over a substrate 500. Thesubstrate 500 may be, for example, a glass substrate such as a bariumborosilicate glass or an alumino borosilicate glass, a quartz substrate,a stainless substrate, or the like. In addition, although a substratemade of flexible synthetic resin such as acrylic or plastic typified byPET, PES, PEN, or the like tends to be inferior to the above substratesin point of the resistance against the heat, the substrate made offlexible synthetic resin can be used when it can resist the heatgenerated in the manufacturing process.

The base film 501 is provided in order to prevent alkali-earth metal oralkali metal such as Na included in the substrate 500 from diffusinginto the semiconductor film. The alkali-earth metal or the alkali metalcauses an adverse effect on the characteristic of the semiconductorelement when it is in the semiconductor. Therefore, the base film isformed of an insulating material such as silicon oxide, silicon nitride,or silicon nitride oxide, which can suppress the diffusion of thealkali-earth metal and alkali metal into the semiconductor film. In thepresent embodiment, a silicon nitride oxide film is formed in thicknessfrom 10 to 400 nm (preferably from 50 to 300 nm) by a plasma CVD method.

It is noted that the base film 501 may be a single insulating film ormay be multilayers of insulating films. In the case of using thesubstrate including the alkali metal or the alkali-earth metal in anyway such as the glass substrate, a SUS substrate, or the plasticsubstrate, it is effective to provide the base film in terms ofpreventing the diffusion of the impurity. When the substrate such as aquartz substrate is used which hardly diffuses the impurity, the basefilm is not always necessary to be provided.

Next, a semiconductor film 502 is formed over the base film 501 inthickness from 25 to 100 nm (preferably from 30 to 60 nm). Thesemiconductor film 502 may be an amorphous semiconductor or apoly-crystalline semiconductor. When the semiconductor film 502 is thepoly-crystalline semiconductor film, the poly-crystalline semiconductorfilm can be recrystallized by the laser irradiation of the presentinvention and a crystalline semiconductor film having a large crystalgrain can be obtained. Moreover, not only silicon but also silicongermanium can be used as the semiconductor. When silicon germanium isused, it is preferable that the density of germanium is in the range ofapproximately 0.01 to 4.5 atomic %.

Next, according to the present invention, the semiconductor film 502 iscrystallized by the laser irradiation as shown in FIG. 7B.

Before the laser crystallization, it is desirable to perform heattreatment to the semiconductor film at 550° C. for four hours in orderto increase the resistance of the semiconductor film 502 against thelaser beam. At the laser crystallization, the continuous wave laseroscillator or the pulsed laser oscillator having the repetitionfrequency of 100 MHz or more can be used.

Specifically, a known continuous wave gas or solid-state laser can beused. The gas laser may be, for example, an Ar laser or Kr laser. Thesolid-state laser may be, for example, a YAG laser, a YVO₄ laser, a YLFlaser, a YAlO₃ laser, a Y₂O₃ laser, a glass laser, a ruby laser, analexandrite laser, or a Ti: Sapphire laser.

The pulse laser having the repetition frequency of 100 MHz or more maybe, for example, an Ar laser, a Kr laser, an excimer laser, a CO₂ laser,a YAG laser, a Y₂O₃ laser, a YVO₄ laser, a YLF laser, a YAlO₃ laser, aglass laser, a ruby laser, an alexandrite laser, a Ti: sapphire laser, acopper vapor laser, or a gold vapor laser.

The crystal having the large grain size can be obtained by, for example,using the second, third, or fourth harmonic of the continuous wavesolid-state laser. Typically, it is desirable to use the second harmonic(532 nm) or the third harmonic (355 nm) of the fundamental wave (1064nm) emitted from the YAG laser. Specifically, the laser beam emittedfrom the continuous wave YAG laser is converted into the harmonic with apower of 4 to 8 W by a non-linear optical element. Then, thequasi-linear beam spot is formed by scanning the beam spot in theuniaxial direction and moved on the semiconductor film 502. The energydensity may be set in the range of 0.01 to 100 MW/cm² (preferably 0.1 to10 MW/cm²). The scanning speed of the laser beam for forming thequasi-linear beam spot is in the range of 1×10⁶ to 1×10⁷ cm/s. In thisembodiment, it is set to 2×10⁶ cm/s. The scanning speed of thequasi-linear beam spot in the direction perpendicular to its major axisis set in the range of 10 to 2000 cm/s. In this embodiment, thecrystallization is performed under the condition where the energy is 5W, the quasi-linear beam spot has a size of 400 μm in the major axis and10 to 20 μm in the minor axis, and the scanning speed in the directionperpendicular to the major axis is set to 35 cm/s.

The interface between the solid phase and the liquid phase can be movedcontinuously by scanning the quasi-linear beam spot in the directionindicated by a white arrow as shown in FIG. 7B. Therefore, the crystalgrain grown continuously in the scanning direction of the quasi-linearbeam spot is formed. By forming the crystal grain of the single crystalextending long in the scanning direction, it is possible to form the TFThaving almost no crystal grain boundaries which intersect the directionwhere the carrier moves.

The laser irradiation may be performed in the inert atmosphere such asnoble gas or nitrogen. This can suppress the roughness of the surface ofthe semiconductor due to the laser irradiation and suppress thevariation of the threshold voltage due to the variation of the interfacestate density.

A semiconductor film 503 in which the crystallinity is further enhancedcan be formed by irradiating the semiconductor film 502 with the laserbeam.

Next, as shown in FIG. 7C, the semiconductor film 503 is patterned toform island-shaped semiconductor films 507 to 509, and varioussemiconductor elements typified by a TFT are formed by using theseisland-shaped semiconductor films 507 to 509.

When the TFT is manufactured for example, a gate insulating film (notshown) is formed so as to cover the island-shaped semiconductor films507 to 509. The gate insulating film may be formed with, for example, asilicon oxide, silicon nitride, or silicon nitride oxide by the plasmaCVD method or the sputtering method.

Next, a gate electrode is formed by forming a conductive film over thegate insulating film and pattering the conductive film. Then, a sourceregion, a drain region, an LDD region, and the like are formed by addingan impurity imparting p-type or n-type conductivity to the island-shapedsemiconductor films 507 to 509 by using the gate electrode or thepatterned resist as the mask.

The TFT can be formed by the above processes. The method formanufacturing the semiconductor device of the present invention is notlimited to the manufacturing method of the TFT described above. Thevariation of the mobility, the threshold voltage, and the on-currentbetween the TFTs can be suppressed when the semiconductor filmcrystallized by the present invention is used as the active layer of theTFT.

Moreover, a crystallization step using a catalyst element may beprovided before the laser crystallization step. The catalyst element maybe, for example, nickel (Ni), germanium (Ge), iron (Fe), palladium (Pd),tin (Sn), lead (Pb), cobalt (Co), platinum (Pt), copper (Cu), or gold(Au). When the crystallization step by the laser beam is performed afterthe crystallization step using a catalyst element, the laser irradiationmelts an upper part of the semiconductor film but does not melt a lowerpart of the semiconductor film. Therefore, a crystal remained withoutbeing melted in the lower part of the semiconductor film becomes acrystal nucleus, and the crystallization is promoted from the lower parttoward the upper part of the semiconductor film. As a result, thecrystallization by the irradiation of the laser beam is promoteduniformly from the side of the substrate to the surface of thesemiconductor film and the crystallinity of the semiconductor film isfurther promoted compared with the case that the crystallization isperformed only by the laser beam. Therefore, the roughness of thesurface of the semiconductor film after the laser crystallization can besuppressed. Consequently, the variation of the characteristic betweenthe semiconductor elements formed afterward, typically the TFT, can besuppressed further, and the off-current can be suppressed.

It is noted that the crystallization may be performed in such a way thatthe heat treatment is performed after the catalyst element is added inorder to promote the crystallization and that the laser irradiation isperformed in order to enhance the crystallinity further. Alternatively,the heat treatment may be omitted. Specifically, after adding thecatalyst element, the laser irradiation may be performed to thesemiconductor film instead of the heat treatment so as to enhance thecrystallinity.

Although the present embodiment has shown an example in which the laserirradiation method of the present invention is used to crystallize thesemiconductor film, the laser irradiation method of the presentinvention may be applied to activate the impurity element doped in thesemiconductor film.

The present embodiment can be freely combined with any one of theembodiment modes 1 to 4 within the possible range.

Embodiment 2

Unlike the embodiment 1, this embodiment describes an example in whichthe laser crystallization is combined with the crystallization by thecatalyst element.

Initially, the process up to forming the semiconductor film 502 isperformed with reference to FIG. 7A of the embodiment 1. Next, as shownin FIG. 8A, a nickel acetate solution including Ni in the range of 1 to100 ppm in weight is applied to the surface of the semiconductor film502 by a spin coating method. It is noted that the catalyst may be addednot only by the above method but also by another method such as asputtering method, an evaporation method, or a plasma process. Next, theheat treatment is performed for 4 to 24 hours at temperatures rangingfrom 500 to 650° C., for example for 14 hours at 570° C. This heattreatment forms a semiconductor film 520 in which the crystallization ispromoted in the vertical direction from the surface with the nickelacetate solution applied thereon toward the substrate 500 (FIG. 8A).

The heat treatment is performed for example at a set temperature of 740°C. for 180 seconds by RTA (Rapid Thermal Anneal) using radiation of thelamp as a heat source or by RTA using heated gas (gas RTA). The settemperature is the temperature of the substrate measured by a pyrometer,and the measured temperature is herein defined as the set temperature inthe heat treatment. As another method, the heat treatment using anannealing furnace at a temperature of 550° C. for 4 hours may be alsoemployed. It is the action of the metal element having the catalyticactivity that lowers the temperature and shortens the time in thecrystallization.

Although the present embodiment uses nickel (Ni) as the catalystelement, another element such as germanium (Ge), iron (Fe), palladium(Pd), tin (Sn), lead (Pb), cobalt (Co), platinum (Pt), copper (Cu), orgold (Au) may be also used.

Subsequently, the semiconductor film 520 is crystallized by the presentinvention as shown in FIG. 8B. The laser crystallization is performedunder the condition described in the embodiment 1.

By the irradiation of the laser beam to the semiconductor film 520 asdescribed above, a semiconductor film 521 in which the crystallinity isenhanced further is formed. It is considered that the semiconductor film521 crystallized using the catalyst element includes the catalystelement (herein Ni) at the density of approximately 1×10¹⁹ atoms/cm³.Therefore, the gettering of the catalyst element existing in thesemiconductor film 521 is performed next.

Initially, an oxide film 522 is formed over a surface of thesemiconductor film 521 as shown in FIG. 8C. By forming the oxide film522 in thickness from approximately 1 to 10 nm, it is possible toprevent the surface of the semiconductor film 521 from becoming rough inthe following etching process. The oxide film 522 can be formed by aknown method. For example, the oxide film 522 may be formed by oxidizingthe surface of the semiconductor film 521 using ozone water or using thesolution in which hydrogen peroxide solution is mixed with sulfuricacid, hydrochloric acid, nitric acid, or the like. Alternatively, theoxide film 522 may be formed by the plasma process, heat treatment, orultraviolet ray irradiation in the atmosphere including oxygen.Moreover, the oxide film 522 may be formed separately by the plasma-CVDmethod, the sputtering method, the evaporation method, or the like.

A semiconductor film 523 for the gettering including the noble gaselement at the density of 1×10²⁰ atoms/cm³ or more is formed inthickness from 25 to 250 nm over the oxide film 522 by the sputteringmethod. It is desirable that the mass density of the semiconductor film523 for the gettering is lower than that of the semiconductor film 521in order to increase the selecting ratio to the semiconductor film 521when being etched. As the noble gas element, one or a plurality ofelements selected from the group consisting of helium (He), neon (Ne),argon (Ar), krypton (Kr), and xenon (Xe) are used.

Next, the gettering is performed by the heat treatment according to thefurnace annealing method or the RTA method. When the furnace annealingmethod is employed, the heat treatment is performed for 0.5 to 12 hoursat temperatures from 450 to 600° C. in the atmosphere of nitrogen. Whenthe RTA method is employed, a lamp light source for heating is turned onfor 1 to 60 seconds, preferably from 30 to 60 seconds, which is repeatedfrom 1 to 10 times, preferably from 2 to 6 times. The luminanceintensity of the lamp light source is set so that the semiconductor filmis heated instantaneously at temperatures ranging from 600 to 1000° C.,preferably from approximately 700 to 750° C.

Through the heat treatment, the catalyst element inside thesemiconductor film 521 is moved to the semiconductor film 523 for thegettering due to the diffusion as indicated by an arrow, and thecatalyst element is thus gettered.

Next, the semiconductor film 523 for the gettering is removed by etchingselectively. The etching process is performed by dry etching using ClF₃not applying plasma or by wet etching using an alkali solution such asthe solution including hydrazine or tetramethylammonium hydroxide(chemical formula (CH₃)₄NOH). On this occasion, the oxide film 522 canprevent the semiconductor film 521 from being etched.

Next, after removing the oxide film 522 by hydrofluoric acid, thesemiconductor film 521 is patterned to form island-shaped semiconductorfilms 524 to 526 (FIG. 8D). Various semiconductor elements, typicallyTFT, can be formed using these island-shaped semiconductor films 524 to526. It is noted that the gettering method is not limited to that shownin this embodiment. Another method may be also employed to decrease thecatalyst element in the semiconductor film.

In this embodiment, the laser irradiation melts an upper part of thesemiconductor film but does not melt a lower part of the semiconductorfilm. Therefore, a crystal remained without being melted in the lowerpart of the semiconductor film becomes a crystal nucleus, and thecrystallization is promoted from the lower part toward the upper part ofthe semiconductor film. As a result, the crystallization by theirradiation of the laser beam is promoted uniformly from the side of thesubstrate to the surface of the semiconductor film, and the crystalorientation is easily aligned. Therefore, the surface is prevented frombecoming rough compared with the case of the embodiment 1. Moreover, thevariation of the characteristic between the semiconductor elementsformed afterwards typically TFT, can be suppressed further.

This embodiment has described the process to promote crystallization byperforming the heat treatment after the catalyst element is added and toenhance crystallinity further by irradiating with the laser beam.However, the present invention is not limited to this, and the heattreatment may be omitted. Specifically, after adding the catalystelement, the laser irradiation may be performed instead of the heattreatment in order to enhance the crystallinity.

This embodiment can be freely combined with any one of the embodimentmodes 1 to 4 and the embodiment 1 within possible range.

Embodiment 3

This embodiment describes another example in which the crystallizationmethod of the present invention is combined with the crystallizationmethod by the catalyst element.

Initially, the process up to forming the semiconductor film 502 isperformed with reference to FIG. 7A of the embodiment 1. Next, a mask540 having an opening is formed over the semiconductor film 502. Then, anickel acetate solution including Ni in the range of 1 to 100 ppm inweight is applied to the surface of the semiconductor film 502. Thecatalyst element may be applied not only by the above method but also bythe sputtering method, the evaporation method, the plasma process, orthe like. The nickel acetate solution contacts the semiconductor film502 in the opening of the mask 540 (FIG. 9A).

Next, a heat treatment is performed for 4 to 24 hours at temperaturesfrom 500 to 650° C., for example for 14 hours at a temperature of 570°C. This heat treatment forms a semiconductor film 530 in which thecrystallization is promoted from the surface with the nickel acetatesolution applied thereon as indicated by a solid-line arrow (FIG. 9A).The heat treatment may be performed not only by the above method butalso by another method such as the method shown in the embodiment 2. Asthe catalyst element, elements recited in the embodiment 2 can be used.

After removing the mask 540, the semiconductor film 530 is crystallizedby the laser irradiation apparatus of the present invention as shown inFIG. 9B. The laser crystallization can be performed under the conditiondescribed in the embodiment 1. By this laser irradiation to thesemiconductor film 530, a semiconductor film 531 in which thecrystallinity is further enhanced is formed.

It is considered that the semiconductor film 531 crystallized using thecatalyst element includes the catalyst element (herein Ni) at thedensity of approximately 1×10¹⁹ atoms/cm³. Therefore, the gettering ofthe catalyst element existing in the semiconductor film 531 is performednext.

Initially, as shown in FIG. 9C, a silicon oxide film 532 for the mask isformed in 150 nm thick so as to cover the semiconductor film 531. Then,the silicon oxide film 532 is patterned to form an opening so that apart of the semiconductor film 531 is exposed. Then, phosphorous isadded to the exposed part of the semiconductor film 531 to form agettering region 533 with the phosphorus added. When heat treatment isperformed in this state for 5 to 24 hours in the nitrogenous atmosphereof 550 to 800° C., for example for 12 hours at a temperature of 600° C.,the gettering region 533 with the phosphorus added works as a getteringsite, and the catalyst element left in the semiconductor film 531 movesto the gettering site 533 with the phosphorous added.

By etching away the gettering region 533 with the phosphorous added, thedensity of the catalyst element can be lowered to be 1×10¹⁷ atoms/cm³ orless in the rest of the semiconductor film 531. Next, after removing thesilicon oxide film 532 for the mask, the semiconductor film 531 ispatterned to form island-shaped semiconductor films 534 to 536 (FIG.9D). These island-shaped semiconductor films 534 to 536 can be used toform various semiconductor elements typified by a TFT. The getteringmethod is not limited to that shown in this embodiment. Another methodmay be also employed to decrease the catalyst element in thesemiconductor film.

In this embodiment, the laser irradiation melts an upper part of thesemiconductor film but does not melt a lower part of the semiconductorfilm. Therefore, a crystal remained without being melted in the lowerpart of the semiconductor film becomes a crystal nucleus, and thecrystallization is promoted from the lower part toward the upper part ofthe semiconductor film. As a result, the crystallization by theirradiation of the laser beam is promoted uniformly from the side of thesubstrate to the surface of the semiconductor film, and the crystalorientation is easily aligned. Therefore, the surface is prevented frombecoming rough compared with the case of the embodiment 1. Moreover, thevariation of the characteristic between the semiconductor elementsformed afterward, typically the TFT, can be suppressed further.

This embodiment can be freely combined with any one of the embodimentmodes 1 to 4 and the embodiments 1 and 2 within possible range.

Embodiment 4

With reference to FIG. 10, this embodiment describes a pixel structureof a light-emitting device, which is one of semiconductor displaydevices that can be manufactured using the laser irradiation apparatus.

In FIG. 10, a base film 6001 is formed over a substrate 6000, and atransistor 6002 is formed over the base film 6001. The transistor 6002has an island-shaped semiconductor film 6003, a gate electrode 6005, anda gate insulating film 6004 sandwiched between the island-shapedsemiconductor film 6003 and the gate electrode 6005.

The island-shaped semiconductor film 6003 is formed with apoly-crystalline semiconductor film that is crystallized by applying thepresent invention. The island-shaped semiconductor film may be formedwith not only silicon but also silicon germanium. When the silicongermanium is used, it is preferable that the density of the germanium isin the range of approximately 0.01 to 4.5 atomic %. Moreover, siliconwith carbon nitride added may be used.

As the gate insulating film 6004, silicon oxide, silicon nitride, orsilicon oxynitride can be used. Moreover, the gate insulating film 6004may be formed by laminating these materials. For example, a film inwhich SiN is formed on SiO₂ may be used as the gate insulating film6004. The gate electrode 6005 is formed with an element selected fromthe group consisting of Ta, W, Ti, Mo, Al, and Cu; or an alloy materialor a chemical compound material including the above element.Furthermore, a semiconductor film typified by a poly-crystalline siliconfilm with an impurity element such as phosphorus doped may be used. Notonly a single conductive film but also a conductive film including aplurality of layers may be used as the gate electrode 6005.

The transistor 6002 is covered with a first interlayer insulating film6006. A second interlayer insulating film 6007 and a third interlayerinsulating film 6008 are formed over the first interlayer insulatingfilm 6006. The first interlayer insulating film 6006 can be formed witha single layer of silicon oxide, silicon nitride, or silicon oxynitrideor formed by laminating the above materials by the plasma CVD method orthe sputtering method.

The second interlayer insulating film 6007 can be formed with an organicresin film, an inorganic insulating film, a siloxane resin, or the like.Note that the siloxane-based resin is defined as resin containingSi—O—Si bond. The siloxane-based resin includes an organic group atleast containing hydrogen (for example, an alkyl group or aromatichydrocarbon) as a substituent. Alternatively, a fluoro group may also beincluded as the substituent. Furthermore, an organic group at leastcontaining hydrogen and a fluoro group may also be included as thesubstituent. In this embodiment, non-photosensitive acrylic is used. Thethird interlayer insulating film 6008 is formed of a film that is hardto transmit the material causing to promote deterioration of thelight-emitting element such as moisture, oxygen, and the like comparedwith another insulating film. Typically, it is preferable to use a DLCfilm, a carbon nitride film, a silicon nitride film formed by the RFsputtering method, or the like.

In FIG. 10, a reference numeral 6010 denotes a first electrode, areference numeral 6011 denotes an electroluminescent layer, a referencenumeral 6012 denotes a second electrode, and the part in which the firstelectrode 6010, the electroluminescent layer 6011, and the cathode 6012are overlapped corresponds to a light-emitting element 6013. One of thetransistors 6002 is a driver transistor for controlling the currentsupplied to the light-emitting element 6013, and it is connecteddirectly or serially through another circuit element to thelight-emitting element 6013. The electroluminescent layer 6011 is asingle light-emitting layer or multilayers including the light-emittinglayer.

The first electrode 6010 is formed over the third interlayer insulatingfilm 6008. An organic resin film 6014 is formed as the partition wall onthe third interlayer insulating film 6008. Although the presentembodiment uses the organic resin film as the partition wall, aninorganic insulating film, a siloxane resin, or the like can be alsoused as the partition wall. The organic resin film 6014 has an opening6015, and the light-emitting element 6013 is formed by overlapping thefirst electrode 6010, the electroluminescent layer 6011, and the secondelectrode 6012 in the opening 6015.

A protective film 6016 is formed over the organic resin film 6014 andthe second electrode 6012. Like the third interlayer insulating film6008, the protective film 6016 is the film that is hard to transmit thematerial causing to promote deterioration of the light-emitting elementsuch as moisture and oxygen. For example, a DLC film, a carbon nitridefilm, a silicon nitride film formed by the RF sputtering method, or thelike is used as the protective film 6016.

It is preferable to make the edge portion of the opening 6015 of theorganic resin film 6014 round so as to prevent the electroluminescentlayer 6011 partially overlapping the organic resin film 6014 fromstaving. More specifically, it is desirable that the sectional surfaceof the organic resin film at the edge of the opening has a radius ofcurvature ranging from approximately 0.2 to 2 μm. With the abovestructure, the coverage of the electroluminescent layer and the secondelectrode to be formed afterward can be improved, and it is possible toprevent the electroluminescent layer 6011 from shorting in the holesformed in the first electrode 6010 and the second electrode 6012.Moreover, when the stress of the electroluminescent layer 6011 isrelaxed, it is possible to decrease the defect called shrink in whichthe light-emitting region decreases and to enhance the reliability.

FIG. 10 shows an example of using positive photosensitive acrylic resinas the organic resin film 6014. The photosensitive organic resinincludes the positive type in which the region where the energy such aslight, electron, or ion is exposed is removed and the negative type inwhich the region that is exposed is not removed. The present inventionmay use the negative organic resin film. Moreover, a photosensitivepolyimide may be used to form the organic resin film 6014. In the caseof forming the organic resin film 6014 using the negative acrylic, theedge portion of the opening 6015 shapes like a letter of S. On thisoccasion, it is desirable that the radius of curvature in the upperportion and the lower portion of the opening is in the range of 0.2 to 2μm.

It is noted that one of the first electrode 6010 and the secondelectrode 6012 is an anode and the other is a cathode.

The anode can be formed with a light-transmitting conductive oxidematerial such as indium tin oxide (ITO), zinc oxide (ZnO), indium zincoxide (IZO), gallium-doped zinc oxide (GZO), or the like. Moreover,indium tin oxide including ITO and silicon oxide (hereinafter referredto as ITSO), or indium oxide including silicon oxide in which zinc oxide(ZnO) is added in the range of 2 to 20% may be used. Furthermore, theanode may be formed with a single layer including one or a plurality ofelements selected from the group consisting of TiN, ZrN, Ti, W, Ni, Pt,Cr, Ag, Al, and the like; two layers formed by laminating a film mainlyincluding titanium nitride and a film mainly including aluminum; threelayers formed by laminating a titanium nitride film, a film mainlyincluding aluminum, and a titanium nitride film; or the like. When theanode is formed of a material different from the light-transmittingconductive oxide material and when the light is emitted from the anodeside, the anode is formed in a thickness of such a degree that the lightcan transmit (preferably from approximately 5 to 30 nm).

The cathode can be formed with metal, an alloy, a conductive compound,or a mixture of these materials each having low work function.Specifically, the cathode can be formed with an alkali metal such as Lior Cs; an alkali-earth metal such as Mg, Ca, or Sr; an alloy includingthese such as Mg:Ag, Al:Li, or Mg:In; a chemical compound of these suchas CaF₂ or CaN; or a rare-earth metal such as Yb or Er. When anelectron-injecting layer is provided in the electroluminescent layer6011, a conductive layer such as Al can be used. When the light isemitted from the cathode side, the cathode may be formed with alight-transmitting conductive oxide material such as the indium tinoxide (ITO), zinc oxide (ZnO), indium zinc oxide (IZO), gallium-dopedzinc oxide (GZO), or the like. Moreover, the cathode may be formed withindium tin oxide including ITO and silicon oxide (hereinafter referredto as ITSO), or indium oxide including silicon oxide in which zinc oxide(ZnO) is further mixed in the range of 2 to 20%. In the case of usingthe light-transmitting conductive oxide material, the electron-injectinglayer is preferably provided to the electroluminescent layer 6011 to beformed afterward. By forming the cathode in the thickness of such adegree that the light can transmit (preferably from approximately from 5to 30 nm), the light can be taken from the cathode side. In this case,the sheet resistance of the cathode may be suppressed by forming thelight-transmitting conductive film with the light-transmittingconductive oxide material so as to contact the upper part or the lowerpart of the cathode.

Although FIG. 10 shows the structure in which the light emitted from thelight-emitting element is delivered to the side of the substrate 6000,the light-emitting element may have a structure in which the light isdelivered to the side opposite to it.

It is noted that after the light-emitting device shown in FIG. 10 isobtained, it is preferable to package (enclose) the light-emittingdevice with a protective film (a film including a layer which can meltwhen applying heat and pressure, ultraviolet curable resin film, or thelike) or a light-transmitting cover member that is highly airtight andhardly degases. The reliability of the light-emitting element isenhanced when the inside of the cover member is filled with the inertatmosphere or the material having moisture-absorption characteristic(barium oxide, for example) is set in the cover member.

Although the present embodiment shows the light-emitting device as anexample of the semiconductor display device, the semiconductor deviceformed by the manufacturing method of the present invention is notlimited to this.

This embodiment can be freely combined with any one of the embodimentmodes 1 to 4 and the embodiments 1 to 3 within possible range.

This application is based on Japanese Patent Application serial no.2004-127468 filed in Japan Patent Office on Apr. 23, 2004, the contentsof which are hereby incorporated by reference.

1. A laser irradiation apparatus comprising: a laser oscillator; anoptical system for forming a quasi-linear beam spot by scanning a laserbeam emitted from the laser oscillator so as to move back and forthalong a straight line; and means for moving a position of an irradiationobject relative to the laser beam in a direction which intersects amajor axis of the quasi-linear beam spot; wherein the irradiation objectis moved by the means so that a first irradiation region irradiated withthe quasi-linear beam spot partly overlaps a second irradiation regionirradiated with the quasi-linear beam spot after the first irradiationregion is irradiated, and wherein a position of the quasi-linear beamspot is moved by the means from the first irradiation region to thesecond irradiation region before the first irradiation region iscompletely solidified.
 2. The laser irradiation apparatus according toclaim 1, wherein the optical system is an acousto-optic element, apolygon mirror, or a resonant scanner.
 3. The laser irradiationapparatus according to claim 1, wherein the laser beam is scanned fasterby the optical system than the irradiation object is moved by the means.4. The laser irradiation apparatus according to claim 1, wherein thelaser oscillator is a pulsed laser oscillator with a repetition rate of100 MHz or more.
 5. The laser irradiation apparatus according to claim1, wherein the laser oscillator is a continuous wave laser oscillator.6. A laser irradiation apparatus comprising: a laser oscillator; anoptical system for scanning a laser beam emitted from the laseroscillator so as to move back and forth along a straight line; and meansfor moving a position of an irradiation object relative to the laserbeam in a direction which intersects a scanning direction of the laserbeam; wherein the laser beam is scanned along a wave-like line or asaw-like line over the irradiation object by the optical system and themeans, wherein when the laser beam is scanned along the wave-like lineor the saw-like line from a first direction-turning point to a thirddirection-turning point through a second direction-turning point, afirst beam spot irradiating the first direction-turning point partlyoverlaps a second beam spot irradiating the third direction-turningpoint, and wherein the laser beam is scanned from the firstdirection-turning point to the third direction-turning point before theirradiation object irradiated with the first beam spot is completelysolidified.
 7. The laser irradiation apparatus according to claim 6,wherein the optical system is an acousto-optic element, a polygonmirror, or a resonant scanner.
 8. The laser irradiation apparatusaccording to claim 6, wherein the laser beam is scanned faster by theoptical system than the irradiation object is moved by the means.
 9. Thelaser irradiation apparatus according to claim 6, wherein the laseroscillator is a pulsed laser oscillator with a repetition rate of 100MHz or more.
 10. The laser irradiation apparatus according to claim 6,wherein the laser oscillator is a continuous wave laser oscillator. 11.A laser irradiation apparatus comprising: a laser oscillator; an opticalsystem for scanning a laser beam emitted from the laser oscillator so asto move back and forth along a straight line; and means for moving aposition of an irradiation object relative to the laser beam in adirection which intersects a scanning direction of the laser beam;wherein the laser beam is scanned along a plurality of straight linesarranging at uniform intervals by the optical system and the means,wherein a first irradiation region irradiated with the laser beam alonga first straight line among the straight lines partly overlaps a secondirradiation region irradiated with the laser beam along a secondstraight line adjacent to the first straight line, and wherein thesecond irradiation region is irradiated with the laser beam before thefirst irradiation region is completely solidified.
 12. The laserirradiation apparatus according to claim 11, wherein the optical systemis an acousto-optic element, a polygon mirror, or a resonant scanner.13. The laser irradiation apparatus according to claim 11, wherein thelaser beam is scanned faster by the optical system than the irradiationobject is moved by the means.
 14. The laser irradiation apparatusaccording to claim 11, wherein the laser oscillator is a pulsed laseroscillator with a repetition rate of 100 MHz or more.
 15. The laserirradiation apparatus according to claim 11, wherein the laseroscillator is a continuous wave laser oscillator.
 16. A laserirradiation apparatus comprising: a laser oscillator; an optical systemfor scanning a laser beam emitted from the laser oscillator so as tomove back and forth along a straight line; and means for moving aposition of an irradiation object relative to the laser beam in adirection which intersects a scanning direction of the laser beam;wherein the laser beam is scanned along a wave-like line or a saw-likeline over the irradiation object by the optical system and the means,wherein when the laser beam is scanned along the wave-like line or thesaw-like line from a first direction-turning point to a thirddirection-turning point through a second direction-turning point, afirst beam spot irradiating the first direction-turning point partlyoverlaps a second beam spot irradiating the third direction-turningpoint, and wherein the laser beam is scanned from the firstdirection-turning point to the third direction-turning point within 100ns.
 17. The laser irradiation apparatus according to claim 16, whereinthe optical system is an acousto-optic element, a polygon mirror, or aresonant scanner.
 18. The laser irradiation apparatus according to claim16, wherein the laser beam is scanned faster by the optical system thanthe irradiation object is moved by the means.
 19. The laser irradiationapparatus according to claim 16, wherein the laser oscillator is apulsed laser oscillator with a repetition rate of 100 MHz or more. 20.The laser irradiation apparatus according to claim 16, wherein the laseroscillator is a continuous wave laser oscillator.
 21. A laserirradiation apparatus comprising: a laser oscillator; an optical systemfor scanning a laser beam emitted from the laser oscillator so as tomove back and forth along a straight line; and means for moving aposition of an irradiation object relative to the laser beam in adirection which intersects a scanning direction of the laser beam;wherein the laser beam is scanned along a plurality of straight linesarranging at uniform intervals by the optical system and the means,wherein a first irradiation region formed by scanning the irradiationobject with the laser beam along a first straight line among thestraight lines partly overlaps a second irradiation region formed byscanning the irradiation object with the laser beam along a secondstraight line adjacent to the first straight line, and wherein the laserbeam is scanned from the first irradiation region to the secondirradiation region within 100 ns.
 22. The laser irradiation apparatusaccording to claim 21, wherein the optical system is an acousto-opticelement, a polygon mirror, or a resonant scanner.
 23. The laserirradiation apparatus according to claim 21, wherein the laser beam isscanned faster by the optical system than the irradiation object ismoved by the means.
 24. The laser irradiation apparatus according toclaim 21, wherein the laser oscillator is a pulsed laser oscillator witha repetition rate of 100 MHz or more.
 25. The laser irradiationapparatus according to claim 21, wherein the laser oscillator is acontinuous wave laser oscillator.
 26. A laser irradiation apparatuscomprising: a laser oscillator; and an optical system for scanning alaser beam emitted from the laser oscillator along a plurality ofstraight lines arranging at uniform intervals; wherein a firstquasi-linear beam spot formed by scanning the laser beam along a firststraight line among the straight lines partly overlaps a secondquasi-linear beam spot formed by scanning the laser beam along a secondstraight line adjacent to the first straight line, and wherein thesecond quasi-linear beam spot is formed by scanning the laser beambefore an irradiation region irradiated with the first quasi-linear beamspot is completely solidified.
 27. The laser irradiation apparatusaccording to claim 26, wherein the optical system comprises a firstoptical system for scanning the laser beam in a first direction and asecond optical system for scanning the laser beam in a direction whichintersects the first direction.
 28. The laser irradiation apparatusaccording to claim 26, wherein each of the first optical system and thesecond optical system is an acousto-optic element, a polygon mirror, ora resonant scanner.
 29. The laser irradiation apparatus according toclaim 26 further comprising: means for moving a position of theirradiation object relative to the laser beam.
 30. The laser irradiationapparatus according to claim 26, wherein the laser oscillator is apulsed laser oscillator with a repetition rate of 100 MHz or more. 31.The laser irradiation apparatus according to claim 26, wherein the laseroscillator is a continuous wave laser oscillator.
 32. A laserirradiation apparatus comprising: a laser oscillator; and an opticalsystem for scanning a laser beam emitted from the laser oscillator alonga plurality of straight lines arranging at uniform intervals; wherein afirst quasi-linear beam spot formed by scanning the laser beam along afirst straight line among the straight lines partly overlaps a secondquasi-linear beam spot formed by scanning the laser beam along a secondstraight line adjacent to the first straight line, and wherein thesecond quasi-linear beam spot begins to be formed by scanning the laserbeam before an irradiation region irradiated with the first quasi-linearbeam spot is completely solidified.
 33. The laser irradiation apparatusaccording to claim 32, wherein the optical system comprises a firstoptical system for scanning the laser beam in a first direction and asecond optical system for scanning the laser beam in a direction whichintersects the first direction.
 34. The laser irradiation apparatusaccording to claim 32, wherein each of the first optical system and thesecond optical system is an acousto-optic element, a polygon mirror, ora resonant scanner.
 35. The laser irradiation apparatus according toclaim 32 further comprising: means for moving a position of theirradiation object relative to the laser beam.
 36. The laser irradiationapparatus according to claim 32, wherein the laser oscillator is apulsed laser oscillator with a repetition rate of 100 MHz or more. 37.The laser irradiation apparatus according to claim 32, wherein the laseroscillator is a continuous wave laser oscillator.
 38. A laserirradiation apparatus comprising: a laser oscillator; and an opticalsystem for scanning a laser beam emitted from the laser oscillator alonga plurality of straight lines arranging at uniform intervals; wherein afirst quasi-linear beam spot formed by scanning the laser beam along afirst straight line among the straight lines partly overlaps a secondquasi-linear beam spot formed by scanning the laser beam along a secondstraight line adjacent to the first straight line, and wherein thesecond quasi-linear beam spot is formed within 100 ns after forming thefirst quasi-linear beam spot.
 39. The laser irradiation apparatusaccording to claim 38, wherein the optical system comprises a firstoptical system for scanning the laser beam in a first direction and asecond optical system for scanning the laser beam in a direction whichintersects the first direction.
 40. The laser irradiation apparatusaccording to claim 38, wherein each of the first optical system and thesecond optical system is an acousto-optic element, a polygon mirror, ora resonant scanner.
 41. The laser irradiation apparatus according toclaim 38 further comprising: means for moving a position of theirradiation object relative to the laser beam.
 42. The laser irradiationapparatus according to claim 38, wherein the laser oscillator is apulsed laser oscillator with a repetition rate of 100 MHz or more. 43.The laser irradiation apparatus according to claim 38, wherein the laseroscillator is a continuous wave laser oscillator.
 44. A laserirradiation apparatus comprising: a laser oscillator; and an opticalsystem for scanning a laser beam emitted from the laser oscillator alonga wave-like line or a saw-like line; wherein when the laser beam isscanned along the wave-like line or the saw-like line from a firstdirection-turning point to a third direction-turning point through asecond direction-turning point, a first beam spot centering on the firstdirection-turning point partly overlaps a second beam spot centering onthe third direction-turning point, and wherein the laser beam is scannedfrom the first direction-turning point to the third direction-turningpoint before an irradiation region irradiated with the first beam spotis completely solidified.
 45. The laser irradiation apparatus accordingto claim 44, wherein the optical system comprises a first optical systemfor scanning the laser beam in a first direction and a second opticalsystem for scanning the laser beam in a direction which intersects thefirst direction.
 46. The laser irradiation apparatus according to claim44, wherein each of the first optical system and the second opticalsystem is an acousto-optic element, a polygon mirror, or a resonantscanner.
 47. The laser irradiation apparatus according to claim 44further comprising: means for moving a position of the irradiationobject relative to the laser beam.
 48. The laser irradiation apparatusaccording to claim 44, wherein the laser oscillator is a pulsed laseroscillator with a repetition rate of 100 MHz or more.
 49. The laserirradiation apparatus according to claim 44, wherein the laseroscillator is a continuous wave laser oscillator.
 50. A laserirradiation apparatus comprising: a laser oscillator; and an opticalsystem for scanning a laser beam emitted from the laser oscillator alonga wave-like line or a saw-like line; wherein when the laser beam isscanned along the wave-like line or the saw-like line from a firstdirection-turning point to a third direction-turning point through asecond direction-turning point, a first beam spot centering on the firstdirection-turning point partly overlaps a second beam spot centering onthe third direction-turning point, and wherein the laser beam is scannedfrom the first direction-turning point to the third direction-turningpoint within 100 ns.
 51. The laser irradiation apparatus according toclaim 50, wherein the optical system comprises a first optical systemfor scanning the laser beam in a first direction and a second opticalsystem for scanning the laser beam in a direction which intersects thefirst direction.
 52. The laser irradiation apparatus according to claim50, wherein each of the first optical system and the second opticalsystem is an acousto-optic element, a polygon mirror, or a resonantscanner.
 53. The laser irradiation apparatus according to claim 50further comprising: means for moving a position of the irradiationobject relative to the laser beam.
 54. The laser irradiation apparatusaccording to claim 50, wherein the laser oscillator is a pulsed laseroscillator with a repetition rate of 100 MHz or more.
 55. The laserirradiation apparatus according to claim 50, wherein the laseroscillator is a continuous wave laser oscillator.
 56. A method ofmanufacturing a semiconductor device comprising: first scanning a firstregion of a semiconductor film with a laser beam along a first directionto melt the first region; and second scanning a second region of thesemiconductor film with the laser beam along a second direction to meltthe second region, after scanning the first region, wherein the firstregion partly overlaps the second region and at least a portion of thefirst region is in a molten state during scanning the second region withthe laser beam.
 57. The method of manufacturing a semiconductor deviceaccording to claim 56, wherein a crystal grows continuously from thefirst region to the second region through a region in which the firstregion overlaps the second region.
 58. The method of manufacturing asemiconductor device according to claim 56, wherein when a part of thesecond region is irradiated with the laser beam, a part of the firstregion overlapped with the second region is in a molten state at leastpartly due to the first scanning of the first region with the laserbeam.
 59. The method of manufacturing a semiconductor device accordingto claim 56, wherein the first region and the second region have alinear shape, and wherein the first direction is the same as the seconddirection and the first region partly overlaps the second region alongthe first direction.
 60. The method of manufacturing a semiconductordevice according to claim 56, wherein the laser beam is emitted from acontinuous wave laser oscillator.
 61. The method of manufacturing asemiconductor device according to claim 56, wherein the laser beam isemitted from a pulsed laser oscillator with a repetition rate of 100 MHzor more.
 62. A method of manufacturing a semiconductor devicecomprising: crystallizing a semiconductor film by irradiating thesemiconductor film with a laser beam; wherein the semiconductor film isscanned with the laser beam along a wave-like line or a saw-like line;wherein when the laser beam is scanned along the wave-like line or thesaw-like line from a first direction-turning point to a thirddirection-turning point through a second direction-turning point, afirst beam spot centering on the first direction-turning point partlyoverlaps a second beam spot centering on the third direction-turningpoint; and wherein the second beam spot is formed by scanning the laserbeam before the semiconductor film irradiated with the first beam spotis completely solidified.
 63. The method of manufacturing asemiconductor device according to claim 62, wherein the laser beam isemitted from a continuous wave laser oscillator.
 64. The method ofmanufacturing a semiconductor device according to claim 62, wherein thelaser beam is emitted from a pulsed laser oscillator with a repetitionrate of 100 MHz or more.
 65. A method of manufacturing a semiconductordevice comprising: crystallizing a semiconductor film by irradiating thesemiconductor film with a laser beam; wherein the semiconductor film isscanned with the laser beam along a comb-like line, wherein when thelaser beam is scanned along the comb-like line from a first angle to afourth angle through second and third angles, a first beam spotcentering on the first angle partly overlaps a second beam spotcentering on the fourth angle, and wherein the second beam spot isformed by scanning the laser beam before the semiconductor filmirradiated with the first beam spot is completely solidified.
 66. Themethod of manufacturing a semiconductor device according to claim 65,wherein the laser beam is emitted from a continuous wave laseroscillator.
 67. The method of manufacturing a semiconductor deviceaccording to claim 65, wherein the laser beam is emitted from a pulsedlaser oscillator with a repetition rate of 100 MHz or more.